This invention relates to contraction joints created in concrete floors and similar monolithic concrete structures which undergo significant shrinkage and contraction-separation upon curing of the concrete of which they are formed. The invention more specifically relates to an improved means for forming a contraction joint which is of small width and whose opposite edges are both protected against spalling.
Concrete floors and similar monolithic structures of the aforesaid type shrink, crack and separate during curing. To prevent such cracking and separation from occurring at random locations within the concrete, it has long been the practice to provide therewithin weakened areas or contraction joints at which contraction-separation of the concrete will occur upon curing thereof. One common way of forming such a contraction joint is by saw-cutting an elongate groove through the upper surface portion of the floor or other concrete structure, after partial curing of the concrete has occurred. Upon further curing, the concrete beneath the groove cracks and the sections of concrete upon opposite sides of a vertical plane extending through the appropriate center of the groove undergo contraction-separation away from each other. The relatively wide space between the separated concrete sections and opposite sides of the groove is then filled with plastic filler material, of which various compositions are commercially available, to complete the contraction joint.
The above-described joint-forming procedure is unsatisfactory in various respects. Sawing grooves within concrete is expensive and tedious work, and requires a return trip to the construction site after the concrete has been poured and allowed to partially cure. If an attempt is made to cut the grooves within the concrete at too early a point in time, the grooves will have undesirably irregular configurations. On the other hand, if too much time is allowed to elapse before the grooves are cut, random cracking and separation of the concrete will occur at locations other than beneath the grooves. Additionally, and perhaps most importantly, the finished contraction joints are relatively wide and do not wear well, particularly when the concrete structure within which they are formed is the floor of a textile mill or similar industrial plant over which there is frequent "traffic" which includes not only pedestrians, but also heavy wheeled vehicles such as fork-lift trucks, dollies, carts, etc. Under such traffic conditions spalling of the opposite upper edges of the construction joints rapidly occurs, even when the joints are filled with plastic filler material.
It has also heretofore been proposed to form a contraction joint by embedding an elongate joint-forming member within the concrete while the same is still in a plastic condition. See, e.g., U.S. Pat. Nos. 1,997,216, 3,023,681, 3,411,260, and 3,555,759. This technique eliminates the above-discussed difficulties inherent in sawing a groove within the concrete after the same has partially cured, but still has not heretofore yielded a finished construction joint which will satisfactorily resist spalling under heavy traffic conditions. Some of the prior-art joint-forming members include a portion or component which is substantially coplanar with the upper surface of the concrete and which upon curing and contraction-separation of the concrete may adhere to and protect the upper edge of one of the two separated concrete sections upon opposite sides thereof. However, the upper edge of the other concrete section remains unprotected after curing and contraction-separation of the concrete, and therefore will undergo spalling when traffic passes over it.
Other prior-art patents of possible relevance to the present invention, although not pertaining to the formation of construction joints of the type presently in question, but rather to the formation of expansion or other types of joints, include the following: U.S. Pat. Nos. 1,001,626, 1,178,700, 1,451,491, 2,405,844, and 3,395,507.